It's interesting that 푸르다 (blue/green) uses a very similar character: 靑, with 青 listed as a variant. Red is the same, 赤 (붉을 적) and yellow (누를 황 / 황색) uses 黃/黄.

Green (녹색) uses 綠. There's also 초록 which is 草綠.

赤: https://hanja.dict.naver.com/#/entry/ccko/ad2ad1893b5c49f8ab...

黃: https://hanja.dict.naver.com/#/entry/ccko/17a2b69699474d5bb8...